Who are the hunters , and what is their job?

The hunters were formerly the Choir. When Ralph is elected leader, he wisely gives control of the Choir to Jack. Jack re-brands them "the hunters". Initially their function was to hunt for meat and keep the signal fire going. By the end of the novel they become simply Jack's soldiers, henchmen or “henchboys” and slaves.

hunt for food and keep the signal fire going

They hunt for food.